Implement `list-templates` CLI command

[nick-pape]

Summary

The dev design specifies a spfx-cli list-templates command that lists all available templates from registered sources. This command does not exist today — only create is implemented.

Requirements

Command signature

spfx list-templates [options]

Flags

Flag	Type	Required	Description
--local-source PATH	string (repeatable)	No	Path(s) to local template folder(s) to include
--remote-source URL	string (repeatable)	No	Public GitHub repo URL(s) to include as template sources

Behavior

• Fetches templates from all registered sources (default GitHub source + any additional local/remote sources)
• Displays a formatted list of templates with: name, description, version, spfxVersion, component category (once Add unit tests for scaffolding API #9 lands)
• Groups or labels by source origin (local vs. remote)

Existing infrastructure

• SPFxTemplateRepositoryManager already supports multiple sources and concurrent fetching
• SPFxTemplateCollection has a toString() method with formatted output
• LocalFileSystemRepositorySource and PublicGitHubRepositorySource are both implemented in @microsoft/spfx-template-api

Implementation notes

• Add a new ListTemplatesAction class in apps/spfx-cli/src/actions/ extending CommandLineAction from @rushstack/ts-command-line
• Register it in SPFxCommandLineParser alongside the existing CreateAction
• Wire up the repository manager with default + user-specified sources

Acceptance criteria

• spfx list-templates lists all templates from default source
• --local-source adds local templates to output
• --remote-source adds remote GitHub templates to output
• Multiple --local-source and --remote-source flags can be combined
• Output is human-readable with template metadata